Laser and photonic chip integration

ABSTRACT

Embodiments herein describe optical assemblies that use a spacer element to attach and align a laser to a waveguide in a photonic chip. Once aligned, the laser can transfer optical signals into the photonic chip which can then perform an optical function such as modulation, filtering, amplification, and the like. In one embodiment, the spacer element is a separate part (e.g., a glass or semiconductor block) that is attached between the photonic chip and a submount on which the laser is mounted. The spacer establishes a separation distance between the photonic chip and the submount which in turn aligns the laser with the waveguide in the photonic chip. In another embodiment, rather than the spacer element being a separate part, the spacer element may be integrated into the submount.

TECHNICAL FIELD

Embodiments presented in this disclosure generally relate to aligning alaser with a photonic chip, and more specifically, to using one or morespacers to align the laser with a waveguide in the photonic chip.

BACKGROUND

Transceivers or other electrical circuitry having integrated opticalcomponents, e.g., a transmit optical subassembly (TOSA) of atransceiver, generally require assembly and attachment of the variouscomponents such as a laser component with electrical and photonicschips. Arranging the individual components to have a small collectivefootprint can provide several benefits such as electrical power savings,improved performance, and a reduced package size.

To minimize the footprint, it may be ideal to attach the laser componentand electrical chip onto the same photonic chip using direct solderconnections. However, in some cases a direct solder attachment is notfeasible, e.g., due to varying temperature requirements for differentsolders and the potential for contaminating the laser component throughreflow and cleaning processes.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate typicalembodiments and are therefore not to be considered limiting; otherequally effective embodiments are contemplated.

FIG. 1 illustrates an optical assembly that includes at least one spacerfor aligning a laser to a photonic chip, according to one embodiment.

FIG. 2 illustrates an optical assembly that includes multiple spacersfor aligning a laser to a photonic chip, according to one embodiment.

FIG. 3 illustrates an optical assembly that includes multiple spacersfor aligning a laser to a photonic chip, according to one embodiment.

FIG. 4 illustrates an optical assembly that includes a submount with aspacer portion for aligning a laser to a photonic chip, according to oneembodiment.

FIG. 5 illustrates an optical assembly that includes at least one spacerfor aligning a laser to a photonic chip, according to one embodiment,

FIG. 6 illustrates an optical assembly that includes at least one spacerfor aligning a laser to a photonic chip, according to one embodiment.

FIG. 7 is a flowchart for aligning a laser to a photonic chip using aspacer, according to one embodiment.

FIGS. 8A-8E illustrate fabrication steps that correspond to theflowchart in FIG. 7, according to one embodiment.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially used in other embodiments withoutspecific recitation.

DESCRIPTION OF EXAMPLE EMBODIMENTS Overview

One embodiment presented in this disclosure is an optical assembly thatincludes a photonic chip comprising at least one waveguide, a submounton which a laser is mounted, and a spacer attached to the photonic chipon a first side and to the submount on a second side, where a thicknessof the spacer aligns the laser such that the laser is edge coupled tothe photonic chip and optically aligned with the at least one waveguide.

Another embodiment described herein is an optical assembly that includesa photonic chip comprising at least one waveguide, a submount on which alaser is mounted where the submount comprises a spacer portion thatextends in a direction away from a surface of the submount on which thelaser is mounted and towards the photonic chip, and where the spacerportion is attached to the photonic chip. Further, a thickness of thespacer portion aligns the laser such that the laser is edge coupled tophotonic chip and optically aligned with the at least one waveguide.

Another embodiment described herein is a method that includes attachinga laser to a first side of a submount, electrically connecting the laserto power rails on the submount, and attaching the submount to a photonicchip using a spacer element that extends away from the first side of thesubmount where the photonic chip comprises at least one waveguide.Further, when attaching the submount to the photonic chip, a thicknessof the spacer element is selected to align the laser such that the laseris edge coupled to the photonic chip and optically aligned with the atleast one waveguide.

Example Embodiments

Embodiments herein describe optical assemblies that use spacers toattach and align a laser to a waveguide in a photonic chip. Oncealigned, the laser can transfer optical signals into the photonic chipwhich can then perform an optical function such as modulation,filtering, amplification, and the like. In one embodiment, the spacer isa separate part (e.g., a glass or semiconductor block) that is attachedbetween the photonic chip and a submount on which the laser is mounted.The spacer establishes a separation distance between the photonic chipand the submount which in turn aligns the laser with the waveguide inthe photonic chip. That is, the thickness of the spacer can be tightlycontrolled so that mounting the spacer between the photonic chip and thesubmount aligns the laser with the waveguide in the photonic chip.

In another embodiment, rather than the spacer being a separate part, thespacer may be integrated into the submount. That is, the submount canhave a spacer portion which extends towards the photonic chip. Thethickness of the spacer portion can align the laser with the photonicchip when the spacer portion is attached to the photonic chip.

Using a spacer element (e.g., a separate spacer or a spacer portionintegrated into the submount) can reduce the size of a cavity which isformed into the photonic chip in order to edge couple the laser with thephotonic chip. That is, without the spacer, the cavity may have to behundreds of microns deep which may require a special etch tool to form.In contrast, using a spacer can reduce the cavity to less than 10microns deep which can be formed using any number of different etchtechniques. Thus, the embodiments herein can greatly reduce the cost andcomplexity of forming a photonic chip that can be edge coupled to alaser.

FIG. 1 illustrates an optical assembly 100 that includes at least onespacer 130 for aligning a laser 150 to a photonic chip 105, according toone embodiment. Specifically, FIG. 1 is a cross sectional side view ofthe optical assembly 100. The photonic chip 105 includes a dielectriclayer 110 (e.g., silicon dioxide or other suitable cladding) thatcontains a waveguide 120 optically coupled to a waveguide adapter 125.The waveguide adapter 125 can include any suitable structure (e.g., aprong structure formed from multiple waveguides, one or more taperingwaveguides, and the like) for improving the optical coupling efficiencybetween the photonic chip 105 and the laser 150. In one embodiment, thewaveguide adapter 125 changes a mode size of the optical signal emittedby the laser 150 to better match a size of the waveguide 120, which maybe a sub-micron waveguide. However, the waveguide adapter 125 is notnecessary and the laser 150 can be directly optically coupled with thewaveguide 120.

Although not shown, the waveguide 120 can transfer the optical signalreceived from the laser 150 to an optical component in the photonic chip105 such as an optical modulator, optical amplifier, optical filter, andthe like. The photonic chip 105 may then transmit the modified opticalsignal to a different optical component, such as transmit the modifiedoptical signal to an optical fiber. In one embodiment, the opticalassembly 100 may be part of a transmitter used to encode digital datainto the optical signal generated by the laser and then transmit theoptical signal to a receiver using an optical fiber.

The photonic chip 105 also includes a semiconductor substrate 115 (e.g.,silicon, a III-V semiconductor, or any other suitable semiconductormaterial) that provides mechanical support to the various opticalcomponents formed in the photonic chip 105. The semiconductor substrate115 may be much thicker than the dielectric layer 110 which is tens ofmicrons while the substrate 115 can be hundreds of microns.

As shown, the photonic chip 105 has been processed to form an etchedfacet 170 and a diced facet 175. In this embodiment, the etched facet170 extends through the dielectric layer 110 and a small portion of thesemiconductor substrate 115 to from a cavity or recess. The diced facet175, in contrast, extends through the entire substrate 115. In oneembodiment, the height of the etched facet 170 (e.g., in the verticaldirection in FIG. 1) is less than 20 microns and can be less than 10microns. In one embodiment, the height of the etched facet 170 is lessthan 50 microns. In one embodiment, the height of the etched facet 170is sufficient to provide clearance for the laser 150 (and any electricalconnections to the laser 150) so that the laser 150 can be edge coupledto the photonic chip 105 at the facet 170. The diced facet 175, on theother hand, may extend entirely through the photonic chip 105, and thus,may have a height of hundreds of microns.

The etched facet 170 can be formed using any suitable etching technique.The diced facet 175 can also be formed using an etching technique, butit might be much more cost and time effective to use a dicing orcleaving technique to form the diced facet 175. Further, while FIG. 1illustrates forming two separate facets in the photonic chip 105, inanother embodiment, dicing or cleaving can be used to form one facetthat extends through the entire photonic chip 105 at which the laser 150can be edge coupled to the waveguide adapter 125.

In FIG. 1, the etched facet 170 provides an optical interface thatpermits the laser 150 and the waveguide adapter 125 and the waveguide120 to transfer optical signals. In one embodiment, the laser 150generates a continuous wave (CW) optical signal that is transmittedthrough the etched facet 170 and into the waveguide adapter 125 and thewaveguide 120. In this example, the waveguide adapter 125 is recessed adistance from the etched facet 170 (e.g., the optical interface)although this is not a requirement.

The spacer 130 is used to align, and mount, the laser 150 to thephotonic chip 105. A first side or surface of the spacer 130 is attachedto a top surface of the photonic chip 105 using one of the connectivelayers 135, while a second, opposite side or surface of the spacer 130is attached to a bottom surface of a submount 140 using another one ofthe connective layers 135. In various embodiments, the connective layers135 are both epoxy layers, or the connective layers 135 both includesolder bumps, or one of the connective layers 135 includes solder bumpsand the other is epoxy. The spacer 130 provides a mechanical connectionbetween the submount 140 and the photonic chip 105. As discussed below,the optical assembly 100 may include multiple spacers 130 for attachingthe submount 140 to the photonic chip 105. In one embodiment, thespacer(s) 130 may be the only part(s) that provide mechanical supportbetween the photonic chip 105 and the submount 140, however in otherembodiments different components can also be used to attach the submount140 to the photonic chip 105.

The spacer 130 may be formed from any material that can be used to alignthe laser 150 to the photonic chip 105. In one embodiment, the materialof the spacer 130 does not expand or contract (or only slightly expandsor contracts) as environmental parameters in which the optical assembly100 operates change. For example, the thickness of the spacer 130 maynot change (or may change only slightly) as the temperature or humidityin the environment the optical assembly 100 operates changes. In oneembodiment, the spacer 130 may be formed from silicon or glass, butthese are just a few of the suitable materials that can be used for thespacer 130.

The submount 140 provides mechanical support to the laser 150 and, alongwith the spacer 130, provides a mechanical connection between the laser150 and the photonic chip 105 so that the laser 150 can be aligned tothe waveguide adapter 125 in the photonic chip 105. In addition toproviding mechanical support, the submount 140 is processed to includeelectrical connections for powering the laser 150. As shown, thesubmount 140 includes contacts 160C-E and vias 145A-B that can transferelectrical power to the laser 150. In this embodiment, the contact 160Eand at least one other contact which is not shown are coupled via wires165B (which form wire bonds) to a contact 160F and at least one othercontact on the photonic chip 105. The contacts on the photonic chip 105can be coupled to power sources which provide power (e.g., at least twovoltages) for powering the laser 150. For example, one voltage isapplied to a top side of the laser 150 by the contact 160E, the via145A, and the contact 160A while another voltage is applied to a bottomside of the laser 150 by the contact 160D, the via 145B, the contact1600. wires 165A (which form wire bonds), and a contact 160B. In thisexample, the contact 160B is disposed on a side of the laser 150 thathas a facing relationship with the photonic chip 105, or morespecifically, with the semiconductor substrate 115 of the photonic chip105.

The electrical components in the submount 140 can be implemented usingmany different techniques to route power from the top surface of thesubmount 140 to its bottom surface on which the laser 150 is attached.As shown, the submount 140 uses the vias 145 to connect electricalcontacts on its top surface to its bottom surface. However, in anotherembodiment, the submount 140 can include “wrap around” contacts thatextend from the top surface, around a side surface, and onto the bottomsurface in order to power the laser 150 using the contact 160A and thewires 165A. In yet another embodiment, the submount 140 can usecastellations formed on one or more sides of the submount 140 totransfer electrical signals from its top surface to its bottom surface.In one embodiment, the castellations have half-moon shapes (when viewedfrom the top) that can either be filled with conductive material, or cansimply be plated with conductive material to provide electricalconnections between the top and bottom surfaces of the submount 140.

In one embodiment, the laser 150 includes a diode (e.g., a P side and anN side) where the power provided by the submount 140 forward-biases thediode in order to generate an optical signal in a laser stripe 155. Thisoptical signal is then transmitted into the waveguide adapter 125 asdiscussed above. In one embodiment, the P side of the laser 150 isbonded to the submount 140 rather than the N side, Thus, the laser 150can be attached to the submount 140 junction side up using solder.

The thickness of the laser 150, and the location of the laser stripe 155within the laser 150, may determine the thickness of the spacer 130.Stated differently, the thickness of the spacer 130 may be set such thatan output of the laser stripe 155 aligns with an input of the waveguideadapter 125. In FIG. 1, the laser 150 is mounted on a same side of thesubmount 140 as the spacer 130. Thus, the thickness of the spacer 130determines a separation distance between the submount 140 and thephotonic chip 105 which in turn determines the alignment of laser stripe155 and the waveguide adapter 125 in the vertical direction. Thethickness of the spacer 130 can be tightly controlled to provide asub-micron tolerance, where the thickness of the spacer 130 varies lessthan +/− one micron. Further, the thicknesses of the connective layers135 (e.g., epoxy, solder, etc.) can also be tightly controller tofacilitate alignment.

In one embodiment, the thickness of the laser 150 can range from 100-150microns. In that case, the thickness of the spacer 130 can range from70-130 microns. However, the thickness of the laser 150, and thus, thethickness of the spacer 130 are not limited to these ranges. Thearrangement shown in FIG. 1 can be adjusted to suit other types of laser150 with different sizes.

Further, the etched facet 170 (and the cavity it forms) providessufficient clearance so that a bottom surface of the laser 150 canextend below the top surface of the photonic chip such that the laser150 is edge coupled to the photonic chip 105. Advantageously, the heightof the etched facet 170 can be small—e.g., less than 50 microns, lessthan 20 microns, or less than 10 microns—which can be formed using manystandard front-of-the-line processes when fabricating the photonic chip105. In contrast, other edge coupling solutions (that do not use thespacer 130) require a deep etch (e.g., hundreds of microns) into thephotonic chip 105 to provide clearance for the laser 150 which cannot bedone using standard front-of-the-line processes and fabrication tools(e.g., a deep reactive ion etch).

FIG. 2 illustrates an optical assembly 200 that includes multiplespacers 130A-B for aligning the laser 150 to a photonic chip 205,according to one embodiment. Specifically, FIG. 2 is a cross sectionalside view of the optical assembly 200. While FIG. 1 illustrates anoptical assembly 100 where only one spacer 130 is used to align thelaser 150 to a photonic chip 105, FIG. 2 illustrates an optical assembly200 where at least two (and possibly more) spacers 130 are used to alignthe laser 150 to a photonic chip 205. As shown, the photonic chip 205 inFIG. 2 is different from the photonic chip 105 in FIG. 1. In FIG. 2, thephotonic chip 205 has been processed to form a different shaped cavity210 that extends through the dielectric layer 110 and a portion of thesemiconductor substrate 115. The cavity 210 can be formed using the sameetching step that was used to form the etched facet 170 in FIG. 1.However, instead of dicing or cleaving the photonic chip 205 a slightdistance to the right of the waveguide adapter 125 (like what was doneto the photonic chip 105 in FIG. 1 to form the diced facet 175), thephotonic chip 205 may be diced or cleaved to the right of the cavity 210such that a support pillar 215 is formed. Thus, the photonic chip 205extends to the right of the laser 150 to form the cavity 210 whichprovides clearance for the laser 150 and to form the support pillar 215on which another spacer 1308 can be attached.

In one embodiment, the top surface of the photonic chip 205 above thewaveguide 120 and the waveguide adapter 125 is coplanar with the topsurface of the support pillar 215. That way, the spacers 130A and 130Bare mounted on the same plane (assuming the thickness of the connectivelayers 135A and 135B are the same). As a result, the top and bottomsurfaces of the submount 240 are substantially parallel with the topsurface of the photonic chip 205 (assuming the connective layers 135 andthe spacers 130 have substantially the same thicknesses relative to eachother).

Using multiple spacers 130 may improve the mechanical connection betweenthe submount 240/laser 150 and the photonic chip 205. That is, disposingspacers 130 on opposite sides of the laser 150 and the cavity 210 candecrease the likelihood that the submount 240 will break off from thephotonic chip 205—e.g., one of the connective layers 135A fails.Further, using multiple spacers 130 may provide greater stability whenaligning the laser 150 to the waveguide adapter 125 during active orpassive alignment stages. For example, during active alignment, analignment machine or technician may press, slide, or rotate the submount240 relative to the photonic chip 205. Using multiple spacers 130 mayprovide more stability during this process.

Further, the spacers 130 in FIGS. 1 and 2 may include epoxy wells thataid the spread of epoxy at the connective layers 135. The epoxy wellscan include parallel slots or circles etched into the spacers 130 (orthe submount 240 and the top surface of the photonic chip 205). In oneembodiment, the epoxy wells help to maintain an even thickness of epoxyin the connective layers and provide space so the spacers 130 can bemoved when actively aligning the laser 150 to the waveguide adapter 125.

While FIG. 2 illustrates two spacers 130, the optical assembly 200 caninclude additional spacers. For example, four spacers 130 may bedisposed at the corners of the cavity 210. Thus, the embodiments hereinare not limited to any particular number of spacers or an arrangement ofthose spacers around the cavity 210.

It may be difficult to make a wire bond connection from the submount 240to the contact 160B given the separation distance between the contact160B and the bottom side of the cavity 210 in the photonic chip 205.Thus, in this embodiment, an electrical contact can be formed betweenthe contact 160B and the contact 160C using a wraparound contact (notshown) on the laser 150 that extends between the contacts 160B and 160C.In one embodiment, the wraparound contact is disposed on an insulatordisposed on a vertical side of the laser 150 so that the laser diode isnot shorted by the wraparound contact.

FIG. 3 illustrates an optical assembly 300 that includes multiplespacers 130 for aligning the laser 150 to a photonic chip 305, accordingto one embodiment. Specifically, FIG. 3 is a top view of an opticalassembly 300 (rather than the side views provided in FIGS. 1 and 2). Forclarity, a submount 340 (on which the laser 150 is mounted) and thephotonic chip 305 are shown in phantom so the underlying components, andtheir arrangement, are visible. That is, FIG. 3 assumes the submount 340and the photonic chip 305 are transparent so that the laser 150, cavity310, waveguide adapter 125, and the waveguide 120 are visible.

In FIG. 3, the spacers 130C and 130D are in facing relationship to oneanother on either side of the cavity 310 formed in part by an etchedfacet 315. This is in contrast to FIGS. 1 and 2 where the spacers wouldbe disposed on the left and/or right sides of the cavity 310 in FIG. 3.Thus, the combination of FIGS. 1-3 illustrates that the spacers 130 canbe disposed on only one side of the laser 150/cavity 210, on a subset ofthe sides of the laser 150/cavity 210, or on all four sides of the laser150/cavity 210.

Further, the spacers 130C and 130D in FIG. 3 can have varying lengths(in the horizontal direction). In this example, the spacers 130 havelengths greater than the length of the laser 150, but in other examplesmay have lengths less than the length of the laser. Further, whilespacers 130 are disposed on opposite sides of the laser 150, in anotherembodiment multiple spacers may be disposed on each side. For example,the spacer 130C may be divided into two or more spacers (and the samefor spacer 130D).

FIG. 4 illustrates an optical assembly 400 that includes a submount 440with a spacer portion 445 for aligning a laser to a photonic chip,according to one embodiment. Instead of having a separate spacer blockas shown in FIGS. 1-3, the submount 440 has the spacer portion 445(e.g., a step) for connecting and aligning the laser 150 to the photonicchip 105, As shown, the photonic chip 105 can be the same as thephotonic chip 105 in FIG. 1, and thus, is not described in detail here.

The optical assembly 400 includes a connective layer 405 (e.g., epoxy,adhesive, solder, etc.) for establishing a mechanical connection betweenthe submount 440 and the photonic chip 105. Like the spacers discussedabove, the spacer portion 445 has a controlled thickness such that whenthe submount 440 is attached to the top surface of the photonic chip105, the laser 150 is aligned with the waveguide adapter 125 and thewaveguide 120. For example, the submount 440 may be processed using oneor more etching steps such that the spacer portion 445 extends away fromthe surface of the submount 440 on which the laser 150 is mounted.

One advantage of using the submount 440 as the spacer is that there isone less connective layer relative to using a separate spacer asdiscussed above, which may simplify the laser alignment process.However, one disadvantage is that controlling the thickness of thespacer portion 445 of the submount 440 may be more difficult thancontrolling the thickness of a separate spacer. For example, if thesubmount 440 is formed from Aluminum Nitride of Silicon, the thicknessmay have a variance of +/−15 microns which can result in poor alignmentbetween the laser 150 and the waveguide adapter 125.

FIG. 5 illustrates an optical assembly that includes a submount 540 withmultiple spacer portions 545 for aligning a laser to a photonic chip205, according to one embodiment. The submount 540 can be mounted on thephotonic chip 205 similar to the one discussed in FIG. 2 that includesthe cavity 210. In this example, the submount 540 includes a spacerportion 545A on one side of the laser 150 (and cavity 210) and a spacerportion 545B on an opposite side of the laser 150 (and cavity 210).Including multiple spacer portions 545 may increase the stability anddurability of the mechanical connection between the submount 540 and thephotonic chip 205 relative to a submount that only has one spacerportion. Further, including multiple spacer portions 545 may improve theability of an alignment tool to align the laser 150 to the photonic chip205, although additional spacer portions 545 may increase the cost ofthe submount 540.

While FIG. 5 illustrates disposing spacer portions 545 to the left andright of the laser 150 and the cavity 210, in other embodiments, thesubmount 540 may include spacer portions in front of and behind thelaser 150 (in the direction in and out of the page). That is, thesubmount 540 may include spacer portions in a similar location as thespacers 130C and 130D illustrated in the top view in FIG. 3. Thesubmount 540 can include spacer portions on all four sides of the laser150, or only a pair of sides. Further, the submount 540 can includemultiple spacer portions on one or more sides. Each of these spacerportions 545 can include a connective layer which provides alignmenttolerance so that the submount 540 can be moved relative to the photonicchip 205 in order to align the laser 150 to the photonic chip 205.Moreover, the spacer portions 545 can have lengths and widths (e.g.,along the left/right directions and in/out of the page) that are lessthan, equal to, or greater than the length and width of the laser 150.

Similar to FIG. 2, it may be difficult to make a wire bond connectionfrom the submount 540 to the contact 160B given the separation distancebetween the contact 160B and the bottom side of the cavity 210 in thephotonic chip 205. Thus, in this embodiment, an electrical contact canbe formed between the contact 160B and the contact 160C using awraparound contact (not shown) on the laser 150 that extends between thecontacts 160B and 160C. In one embodiment, the wraparound contact isdisposed on an insulator disposed on a vertical side of the laser 150 sothat the laser diode is not shorted by the wraparound contact.

FIG. 6 illustrates an optical assembly 600 that includes at least onespacer 130 for aligning a laser 650 to a photonic chip 605, according toone embodiment. In this example, the photonic chip 605 is fabricated toinclude pillars 660 for supporting and aligning the laser 650. Forexample, when etching a cavity 610 into the photonic chip 605, the etchcan be patterned so that one or more pillars 660 are formed. In oneembodiment, the pillars 660 may be formed within the cavity 610.However, in another embodiment, the pillars 660 may be formed on theedges of the cavity 610. That is, the pillars 660 can be standalonefeatures in the cavity 610 or can have one or more sides that are partof a boundary of the cavity 610.

In turn, the laser 650 is processed to include receptacles 655 that matewith the pillars 660 in the photonic chip 605. That is, the receptacles655 can define apertures with dimensions that substantially match thedimensions of the pillars 660 so that the pillars can be fitted withinthe apertures. In this manner, the optical assembly 600 can use thepillars 660 and the receptacles 655 along with the spacer 130 to alignthe laser 650 to the waveguide adapter 125. In one embodiment, matingthe receptacles 655 with the pillars 660 aids to align the laser 650 insix degrees (or six axes) of freedom. These features can be used inactive and passive alignment steps.

Further, the receptacles 655 and the pillars 660 can also be used in theother types of optical assemblies discussed above. For example, thereceptacles 655 and the pillars 660 can be added to the opticalassemblies that include multiples spacers as shown in FIGS. 2 and 3(rather than just one spacer as shown in FIG. 6). Further, thereceptacles 655 and the pillars 660 can be used with the opticalassemblies in FIGS. 4 and 5 that include submounts with integratedspacer portions, rather than separate spacers.

FIG. 7 is a flowchart of a method 700 for aligning a laser to a photonicchip using a spacer, according to one embodiment. For clarity, some ofthe blocks in the method 700 are discussed in tandem with FIGS. 8A-8Ewhich illustrate fabrication steps corresponding to the flowchart inFIG. 7, according to one embodiment.

At block 705, a laser is attached to a submount. As shown in FIG. 8A,the laser 150 is attached to the contact 160A of the submount 140. Thecontacts 160 can be formed from any conductive metal such as gold, tin,or a combination thereof. In one embodiment, the laser 150 is solderedto the contact 160A but any suitable connection technique can be used toelectrically, and mechanically, couple the laser 150 to the contact160A,

At block 710, the laser is electrically connected to power rails on thesubmount. As shown in FIG. 8B, the laser 150 is electrically connectedto the submount 140 using two contacts: contact 160A and 160B. Theelectrical connection to the contact 160A is made directly whenperforming block 705. However, to electrical connect the contact 160B onthe opposite side of the laser 150 to the submount 140, the wires 165Aare used to form wire bonds between the contact 160B and the contact160C.

Although not shown in FIG. 8B, the submount 140 includes electricalconnections between a first side 805 on which the laser 150 is attachedand a second, opposite side 810 of the submount 140. As mentioned above,these electrical connections can include vias that extend through thesubmount 140, castellations at the edge of the submount 140, or wraparound contacts that extend from the first side 805 to the second side810. That is, these electrical connections can connect the contacts 160Aand 160C to contacts 160D and 160E on the second side 810. The contacts160D and 160E can serve as power rails to provide power signals (e.g.,different voltages) for driving the laser 150.

At block 715, the laser is tested. In one embodiment, the power rails onthe submount can be temporarily connected to a testing apparatus using,e.g., test probes, that powers the laser. The testing apparatus can thenensure the laser is functioning properly. Advantageously, being able totest the laser before it is attached to the photonic chip can improveyield and reduce costs since non-functioning lasers can be identifiedbefore they are attached to a photonic chip. If a laser is tested afterbeing attached to a photonic chip, then the entire optical assembly(including the photonic chip) may be unusable (or have to be recycled)if the laser is then determined as being non-functional.

Assuming the laser is functional, at block 720 a spacer is attached to afirst side of a photonic chip. As shown in FIG. 8C, the spacer 130 isattached to the photonic chip 105 using the connective layer 135A. Forexample, if the connective layer 135A is epoxy, the spacer 130 can bedisposed on uncured epoxy and then cured before the spacer is thenattached to the submount. However, in another embodiment, the epoxy inthe layer 135A may remain uncured until after the spacer 130 is attachedto the submount.

At block 725, a second side of the spacer (opposite the first side) isattached to the submount. As shown in FIG. 8D, a connective layer 135B(e.g., epoxy or solder balls) are applied to the second side of thespacer 130 that is opposite the first side of the spacer 130 connectedto the layer 135A. However, in another embodiment, the connective layer135B may instead be applied to the submount 140. In either case, thesubmount 140 is attached to the second side of the spacer 130 using theconnective layer 135B.

In one embodiment, before curing the epoxy or when reflowing the solderin the connective layer 135B, one or more alignment steps (e.g., activealignment steps) are performed to align the laser 150 with the waveguideelements (e.g., the waveguide adapter) in the photonic chip 105.However, in other embodiments, the laser 150 may be aligned using onlypassive alignment steps. For example, if the laser 150 and the photonicchip 105 includes the receptacles 655 and pillars 660 illustrated inFIG. 6, active alignment may not be used. Further, if multiple spacers130 are used (rather than just one as shown in FIG. 8D), activealignment may not be used. However, in other embodiments, even when thereceptacles 655, pillars 660, and multiple spacers 130 are used, activealignment steps may be used to align the laser 150 and the photonic chip105 when at least one (but possibly both) of the connective layers 135is in an liquid state (e.g., uncured epoxy or when solder has beenmelted).

At block 730, the power rails in the submount are electrically connectedto power sources. In the example shown in FIG. 8E, the contact 160E (aswell as other contacts not shown) is wire bonded to the contact 160F(and potentially other contacts) on the photonic chip 105 using thewires 165B. The contact 160F, in turn, can be electrically connected toa laser driver (e.g., a power source) which generates the power for thelaser 150. In one embodiment, the laser driver can be mounted on (orintegrated in) the photonic chip 105. In another embodiment, thephotonic chip 105 can be electrically connected (using additional wirebonds or a solder connection) to an electrical IC that includes thelaser driver.

While the examples in FIGS. 8A-8D were primarily focused on assemblingan optical assembly that includes a single, separate spacer, the method700 can also be modified for any of the embodiments illustrated in FIGS.2-6. For example, instead of attaching a single spacer at blocks 720 and725 to the photonic chip and submount, multiple spacers can be attachedduring those blocks. Further, if a submount with an integrated spacerportion is used (rather than separate spacers), block 720 may be omittedsince the spacer portion is already integrated into the submount.Instead, in that example, the spacer portion of the submount is attachedto the photonic chip using a connective layer. A separate spacer (e.g.,as shown in FIGS. 1-3) and the integrated spacer portion (e.g., as shownin FIGS. 4-5) can be collectively referred to as “spacer elements” whosethicknesses are set to align the laser such that the laser is edgecoupled to photonic chip and optically aligned with the at least onewaveguide in the photonic chip.

In the current disclosure, reference is made to various embodiments.However, the scope of the present disclosure is not limited to specificdescribed embodiments. Instead, any combination of the describedfeatures and elements, whether related to different embodiments or not,is contemplated to implement and practice contemplated embodiments.Additionally, when elements of the embodiments are described in the formof “at least one of A and B,” it will be understood that embodimentsincluding element A exclusively, including element B exclusively, andincluding element A and B are each contemplated. Furthermore, althoughsome embodiments disclosed herein may achieve advantages over otherpossible solutions or over the prior art, whether or not a particularadvantage is achieved by a given embodiment is not limiting of the scopeof the present disclosure. Thus, the aspects, features, embodiments andadvantages disclosed herein are merely illustrative and are notconsidered elements or limitations of the appended claims except whereexplicitly recited in a claim(s). Likewise, reference to “the invention”shall not be construed as a generalization of any inventive subjectmatter disclosed herein and shall not be considered to be an element orlimitation of the appended claims except where explicitly recited in aclaim(s).

It should be noted that, in some alternative implementations, thefunctions noted in the block may occur out of the order noted in theFigures. For example, two blocks shown in succession may, in fact, beexecuted substantially concurrently, or the blocks may sometimes beexecuted in the reverse order, depending upon the functionalityinvolved.

In view of the foregoing, the scope of the present disclosure isdetermined by the claims that follow.

1. An optical assembly, comprising: a photonic chip comprising at leastone waveguide; a submount on which a laser is mounted, wherein thephotonic chip comprises an etched facet creating a cavity in thephotonic chip, wherein the laser is disposed within the cavity, whereinthe cavity comprises at least one pillar extending in a directiontowards the laser and the submount, wherein the laser comprises at leastone receptacle that mates with the at least one pillar; and a spacerattached to the photonic chip on a first side of the spacer and to thesubmount on a second side of the spacer, wherein a thickness of thespacer aligns the laser such that the laser is edge coupled to thephotonic chip and optically aligned with the at least one waveguide. 2.The optical assembly of claim 1, wherein the spacer is attached to thephotonic chip via a first connective layer and is attached to thesubmount via a second connective layer.
 3. The optical assembly of claim1, wherein the spacer is attached to a same side of the submount as thelaser.
 4. (canceled)
 5. The optical assembly of claim 1, wherein theetched facet provides an optical interface configured to permit opticalsignals to be transferred between the laser and the at least onewaveguide.
 6. (canceled)
 7. The optical assembly of claim 1, wherein thelaser includes a first electrical connection to the submount via a firstcontact disposed between the laser and the submount and a secondelectrical connection to the submount via a wire bond between a side ofthe laser in a facing relationship with the photonic chip and a secondcontact on the submount.
 8. The optical assembly of claim 1, furthercomprising: a second spacer attached to the photonic chip on a firstside of the second spacer and to the submount on a second side of thesecond spacer, wherein a thickness of the second spacer aligns the lasersuch that the laser is edge coupled to the photonic chip and opticallyaligned with the at least one waveguide.
 9. The optical assembly ofclaim 8, wherein the photonic chip comprises a cavity in which the laseris disposed, wherein the spacer and the second spacer are disposed onopposite sides of the cavity.
 10. An optical assembly, comprising: aphotonic chip comprising at least one waveguide; and a submount on whicha laser is mounted, wherein the submount comprises a spacer portionhaving a thickness between a surface of the submount on which the laseris mounted and the photonic chip, wherein the spacer portion is attachedto the photonic chip, wherein the photonic chip comprises an etchedfacet creating a cavity in the photonic chip and the laser is disposedwithin the cavity, wherein the cavity comprises at least one pillarextending in a second direction towards the laser and the submount,wherein the laser comprises at least one receptacle that mates with theat least one pillar, wherein the thickness of the spacer portion isselected to align the laser such that the laser is edge coupled to thephotonic chip and optically aligned with the at least one waveguide. 11.(canceled)
 12. The optical assembly of claim 10, wherein the etchedfacet provides an optical interface configured to permit optical signalsto be transferred between the laser and the at least one waveguide. 13.(canceled)
 14. The optical assembly of claim 10, wherein the laserincludes a first electrical connection to the submount via a firstcontact disposed between the laser and the submount and a secondelectrical connection to the submount via a wire bond between a side ofthe laser in a facing relationship with the photonic chip and a secondcontact on the submount.
 15. The optical assembly of claim 10, whereinthe submount comprises a second spacer portion that extends in adirection away from the surface of the submount on which the laser ismounted and towards the photonic chip, wherein the second spacer portionis attached to the photonic chip, wherein a thickness of the secondspacer portion aligns the laser such that the laser is edge coupled tothe photonic chip and optically aligned with the at least one waveguide.16. The optical assembly of claim 15, wherein the photonic chipcomprises a cavity in which the laser is disposed, wherein the spacerportion and the second spacer portion are disposed on opposite sides ofthe cavity. 17-20. (canceled)
 21. An optical assembly, comprising: aphotonic chip comprising at least one waveguide; a submount on which alaser is mounted; and a spacer is attached to the photonic chip on afirst side of the spacer by a first connective layer and to the submounton a second side of the spacer by a second connective layer, wherein athickness of the spacer aligns the laser such that the laser is edgecoupled to the photonic chip and optically aligned with the at least onewaveguide, and wherein the spacer and the laser are mounted on a samesurface of the submount.
 22. The optical assembly of claim 21, whereinthe spacer is attached to the photonic chip via a first connective layerand is attached to the submount via a second connective layer.
 23. Theoptical assembly of claim 21, wherein the photonic chip comprises anetched facet creating a cavity in the photonic chip, wherein the laseris disposed within the cavity.
 24. The optical assembly of claim 23,wherein the etched facet provides an optical interface configured topermit optical signals to be transferred between the laser and the atleast one waveguide.
 25. The optical assembly of claim 21, wherein theetched facet provides an optical interface configured to permit opticalsignals to be transferred between the laser and the at least onewaveguide.
 26. The optical assembly of claim 21, wherein the laserincludes a first electrical connection to the submount via a firstcontact disposed between the laser and the submount and a secondelectrical connection to the submount via a wire bond between a side ofthe laser in a facing relationship with the photonic chip and a secondcontact on the submount.
 27. The optical assembly of claim 21, furthercomprising: a second spacer attached to the photonic chip on a firstside of the second spacer and to the submount on a second side of thesecond spacer, wherein a thickness of the second spacer aligns the lasersuch that the laser is edge coupled to the photonic chip and opticallyaligned with the at least one waveguide.
 28. The optical assembly ofclaim 27, wherein the photonic chip comprises a cavity in which thelaser is disposed, wherein the spacer and the second spacer are disposedon opposite sides of the cavity.